Two recent developments suggest that China is preparing to take preemptive action in the South China Sea in advance of the ruling by the Arbitral Tribunal at the Permanent Count of Arbitration (PCA) in The Hague on claims against it brought by the Philippines. (That ruling is expected in late-May or June.)

These developments include beefing up air defenses on Woody Island in the Paracels, and, moreover, leaked intelligence assessments that China may be planning major construction activities at Scarborough Shoal…

There are three likely explanations for China’s action.

First, China is reacting to the activation of the Enhanced Defense Cooperation Agreement between the Philippines and the United States.

China also is angered at the current Balikatan (Shoulder-to-Shoulder) military exercises underway in the Philippines involving U.S., Australian, and other military forces and the accompanying visit by U.S. Defense Secretary Ashton Carter to the Philippines…

Second, China also may be reacting to recent reports that the next U.S. Freedom of Navigation Operational Patrol in the South China Sea will take place shortly, following a first operation in the Spratlys in October 2015 and another in the Paracels in January 2016.

We express our strong opposition to any intimidating, coercive or provocative unilateral actions that could alter the status quo and increase tensions, and urge all states to refrain from such actions as land reclamations including large scale ones, building of outposts, as well as their use for military purposes and to act in accordance with international law including the principles of freedoms of navigation and overflight.

China has constructed and continues to construct helipads on its occupied features. This would enable China to monitor U.S. submarines through the deployment of aerial reconnaissance aircraft and anti-submarine warfare helicopters.

If China undertakes “decisive and provocative” action by shoring up its position on Scarborough Shoal, it would present a fait accompli to findings of the Arbitral Tribunal. The Tribunal has no power of enforcement. China’s pre-emptive actions would likely derail any concerted action by the international community to exert diplomatic pressure on China to respect international law by accepting the findings of the Arbitral Tribunal. Concerns about international law would be sidelined by China’s newest phase of militarization.